Laser diode device with a plurality of gallium and nitrogen containing substrates

ABSTRACT

In an example, the present invention provides a gallium and nitrogen containing multilayered structure, and related method. The structure has a plurality of gallium and nitrogen containing semiconductor substrates, each of the gallium and nitrogen containing semiconductor substrates (“substrates”) having a plurality of epitaxially grown layers overlaying a top-side of each of the substrates. The structure has an orientation of a reference crystal direction for each of the substrates. The structure has a first handle substrate coupled to each of the substrates such that each of the substrates is aligned to a spatial region configured in a selected direction of the first handle substrate, which has a larger spatial region than a sum of a total backside region of plurality of the substrates to be arranged in a tiled configuration overlying the first handle substrate. The reference crystal direction for each of the substrates is parallel to the spatial region in the selected direction within 10 degrees or less. The structure has a first bonding medium provided between the first handle substrate and each of the substrate while maintaining the alignment between reference crystal orientation and the selected direction of the first handle substrate; and a processed region formed overlying each of the substrates configured concurrently while being bonded to the first handle substrate. Depending upon the embodiment, the processed region can include any combination of the aforementioned processing steps and/or steps.

CROSS-REFERENCES TO RELATED APPLICATIONS

The present application is a divisional of U.S. application Ser. No.14/175,622, filed Feb. 7, 2014, the entire contents of which areincorporated herein by reference in their entirety for all purposes.

BACKGROUND

In 1960, the laser was first demonstrated by Theodore H. Maiman atHughes Research Laboratories in Malibu. This laser utilized asolid-state flash lamp-pumped synthetic ruby crystal to produce redlaser light at 694 nm. By 1964, blue and green laser output wasdemonstrated by William Bridges at Hughes Aircraft utilizing a gas laserdesign called an Argon ion laser. The Ar-ion laser utilized a noble gasas the active medium and produce laser light output in the UV, blue, andgreen wavelengths including 351 nm, 454.6 nm, 457.9 nm, 465.8 nm, 476.5nm, 488.0 nm, 496.5 nm, 501.7 nm, 514.5 nm, and 528.7 nm. The Ar-ionlaser had the benefit of producing highly directional and focusablelight with a narrow spectral output, but the wall plug efficiency was<0.1%, and the size, weight, and cost of the lasers were undesirable aswell.

As laser technology evolved, more efficient lamp pumped solid statelaser designs were developed for the red and infrared wavelengths, butthese technologies remained a challenge for blue and green and bluelasers. As a result, lamp pumped solid state lasers were developed inthe infrared, and the output wavelength was converted to the visibleusing specialty crystals with nonlinear optical properties. A green lamppumped solid state laser had 3 stages: electricity powers lamp, lampexcites gain crystal which lases at 1064 nm, 1064 nm goes into frequencyconversion crystal which converts to visible 532 nm. The resulting greenand blue lasers were called “lamped pumped solid state lasers withsecond harmonic generation” (LPSS with SHG) had wall plug efficiency of˜1%, and were more efficient than Ar-ion gas lasers, but were still tooinefficient, large, expensive, fragile for broad deployment outside ofspecialty scientific and medical applications. Additionally, the gaincrystal used in the solid state lasers typically had energy storageproperties which made the lasers difficult to modulate at high speedswhich limited its broader deployment.

To improve the efficiency of these visible lasers, high power diode (orsemiconductor) lasers were utilized. These “diode pumped solid statelasers with SHG” (DPSS with SHG) had 3 stages: electricity powers 808 nmdiode laser, 808 nm excites gain crystal, which lases at 1064 nm, 1064nm goes into frequency conversion crystal which converts to visible 532nm. The DPSS laser technology extended the life and improved the wallplug efficiency of the LPSS lasers to 5-10%, and furthercommercialization ensue into more high-end specialty industrial,medical, and scientific applications. However, the change to diodepumping increased the system cost and required precise temperaturecontrols, leaving the laser with substantial size, power consumptionwhile not addressing the energy storage properties which made the lasersdifficult to modulate at high speeds.

As high power laser diodes evolved and new specialty SHG crystals weredeveloped, it became possible to directly convert the output of theinfrared diode laser to produce blue and green laser light output. These“directly doubled diode lasers” or SHG diode lasers had 2 stages:electricity powers 1064 nm semiconductor laser, 1064 nm goes intofrequency conversion crystal which converts to visible 532 nm greenlight. These lasers designs are meant to improve the efficiency, costand size compared to DPSS-SHG lasers, but the specialty diodes andcrystals required make this challenging today. Additionally, while thediode-SHG lasers have the benefit of being directly modulate-able, theysuffer from severe sensitivity to temperature which limits theirapplication. Currently the only viable direct blue and green laser diodestructures are fabricated from the wurtzite AlGaInN material system. Themanufacturing of light emitting diodes from GaN related materials isdominated by the heteroeptiaxial growth of GaN on foreign substratessuch as Si, SiC and sapphire. Laser diode devices operate at such highcurrent densities thatThe crystalline defects associated withheteroepitaxial growth are not acceptable in laser diode devices due tothe high operational current densities found in laser diodes. Because ofthis, very low defect-density, free-standing GaN substrates have becomethe substrate of choice for GaN laser diode manufacturing.

From the above, techniques for improving laser diodes are highlydesirable.

SUMMARY

The invention is directed the method of fabrication of optoelectronicdevices from semiconductor wafers. In particular, the invention providesa method and device for emitting electromagnetic radiation usingnonpolar or semipolar gallium containing substrates such as GaN, AN,InN, InGaN, AlGaN, and AlInGaN, and others. The invention provides amethod and device using a gallium and nitrogen containing substrate ofthe wurtzite crystal structure configured on any of the (0001), {11-20},{10-10}, {10-11}, {20-21} and {30-31} families of crystal planes or anoffcut of any of these planes according to one or more embodiments, butthere can be other configurations. For example, it is possible undercertain circumstances to produce gallium and nitrogen containingsubstrates with zincblende crystal structures which would be applicableunder this invention. Still more particularly, this invention provides amethod for processing small semiconductor wafers or non-standard sizesuch that all multiple wafers can be processed in parallel at themajority of steps in the fabrication process. As used herein the term“small” generally means smaller than a handle substrate, although therecan be other meanings used by one of ordinary skill in the art. Theinvention can be applied to optical devices such as lasers and lightemitting diodes, among other devices.

This invention provides for the bonding of multiple small-areasemiconductor wafers to a “carrier” or “handle” wafer such that thecrystallographic directions of the semiconductor wafers are nominallyaligned. In other examples, as defined herein a small area substrate isdefined as a semiconductor wafer that is less than 2000 mm² in area andwhich may have a rectangular or square shape that is not typicallyencountered in semiconductor technology. In a preferred embodiment thesmall area substrates are aligned such that the crystallographicdirections of the small area substrates deviate from one another by 1degree or less. In a second embodiment the small area substrates arealigned such that the crystallographic directions of the small areasubstrates deviate from one another by 5 degrees or less. Bonding isachieved either using an organic adhesive or wax, photo-resist,spin-on-glass or other materials sinterable at low temperatures,metal-metal thermo-compressive bonding, oxide-oxide bonding or bondingwith a solder. The invention provides for the small area substrates tobe aligned relative to each other with known position or spacing. In apreferred embodiment this is achieved by patterning the handle waferwith alignment marks or with discontinuous bond pads that determine thespacing between small area substrates.

This example provides for the processing of the unbonded side of thesmall area substrates. Processing steps include metal depositions,annealing, dry and wet etches, deposition of passivation layers such asoxides and nitrides, deposition of planarizing polymers or spin-on-glassand others. Moreover, this example provides for the bonding of the smallarea substrates as an ensemble to a second handle wafer and thesubsequent removal of the first handle wafer such that thecrystallographic alignment and in-plane spacing of the small wafersremains unchanged. Backside processing can be performed, such as waferthinning via lapping, grinding or chemical etching, metal and dielectricdeposition, laser scribing and mechanical scribing among others. Thisexample provides for a third bonding of the small area substrates as anensemble to a third handle wafer and the subsequent removal of thesecond handle wafer. In the preferred embodiment, the final handleshould be a single crystal wafer capable of being cleaved alongcrystallographic planes. In this preferred embodiment the individualrows of lasers are singulated into composite bars that are composed of anarrow section of the handle wafer bonded to narrow sections of one ormore of the small area substrates which are themselves composed of alinear array of laser die. In a preferred embodiment these compositebars are used to carry out final process steps on laser bars includingdeposition of reflective coatings on back facets and deposition ofreflective or anti-reflective coatings on front facets.

Additional benefits are achieved over pre-existing techniques using theinvention. In particular, the invention enables a cost-effective opticaldevice for laser applications. In a specific embodiment, the presentoptical device can be manufactured in a relatively simple and costeffective manner. Depending upon the embodiment, the present apparatusand method can be manufactured using conventional materials and/ormethods according to one of ordinary skill in the art. The present laserdevice uses a non-polar or semipolar gallium nitride material capable ofachieve a blue or green laser device, among others. In one or moreembodiments, the laser device is capable of emitting long wavelengthssuch as those ranging from about 480 nm to greater than about 540 nm,but can be others such as 540 nm to 660 nm and 420 to 480 nm. Dependingupon the embodiment, one or more of these benefits may be achieved. Ofcourse, there can be other variations, modifications, and alternatives.

A further understanding of the nature and advantages of the inventionmay be realized by reference to the latter portions of the specificationand attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified illustration of a handle wafer with several smallarea substrates according to an example of the present invention.

FIG. 2 is a simplified illustration of a handle wafer bonded to smallarea substrates using a bonding media in an example according to thepresent invention.

FIG. 3 is a simplified illustration of a handle wafer bonded to smallarea substrates using a bonding media that has been deposited onto thehandle wafer in a pattern in an example according to the presentinvention.

FIG. 4 is a simplified illustration of a handle wafer bonded to severalsmall area substrates according to an example of the present invention.

FIG. 5 is a simplified illustration of azimuthal (i.e. in-plane angular)alignment of many small area wafers according to an example of thepresent invention.

FIG. 6 is a simplified illustration of cleaving of bonded wafers as anensemble in an example of the present invention.

FIG. 7 is a simplified illustration of bonding from examples structures.

FIG. 8A illustrates laser diode device wafer including GaN substratelayer, n-type cladding, light emitting layers and p-type cladding in anexample of the present invention.

FIG. 8B illustrates ridges, passivation layers and electrical contactshave been fabricated into the epitaxial layers of the laser device waferin an example of the present invention.

FIG. 8C: Laser device wafer, bonded to second handle. Backsideelectrical contact layers 313 overlaid on backside of thinned substratelayer. The device wafer is subsequently debonded from the second handleand cleaved into bars.

FIG. 9: Schematic diagram of semipolar laser diode with the cavityaligned in the projection of c-direction with cleaved or etched mirrorsaccording to an example of the present invention.

FIG. 10: Schematic cross-section of ridge laser diode according to anexample of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The invention provides a method for fabricating an optical device, e.g.,laser, LED. Typically these devices are fabricated on one substrate at atime. What follows is a general description of the typical configurationand fabrication of these devices.

However, as further background, gallium nitride, and related crystalsare difficult to produce in bulk form. Growth technologies capable ofproducing large area boules of GaN are still in the infancy. While largearea, free-standing GaN substrates (e.g. with diameters of two inches orgreater) are available commercially, the availability of large areanon-polar and semi-polar GaN substrates is quite restricted. Typically,these orientations are produced by the growth of a c-plane orientedbool, which is then sliced into rectangular wafers at some steep anglerelative to the c-plane. The width of these wafers is limited by thethickness of the c-plane oriented bool, which in turn is restricted bythe method of boule production (e.g. typically hydride vapor phaseepitaxy (HVPE) on a foreign substrate). Such small wafer sizes arelimiting in two respects. The first is that epitaxial growth must becarried out on such a small wafer, which increases the area fraction ofthe wafer that is unusable due to non-uniformity in growth near thewafer edge. The second is that after epitaxial growth of optoelectronicdevice layers on a substrate, the same number of processing steps arerequired on the small wafers to fabricate the final device as one woulduse on a large area wafer. Both of these effects drive up the cost ofmanufacturing devices on such small wafers, as both the cost per devicefabricated and the fraction of wafer area that is unusable increaseswith decreasing wafer size.

Processing of multiple wafers in parallel could help reduce these costs,however it requires that the wafers be connected together into a singleunit. This can be achieved by bonding the wafers to another object thatcan be used as a “carrier” or “handle” in order to form a compositestructure. Semiconductor lasers exhibit a challenge in that devices arecommonly singulated from a semiconductor wafer by the cleaving of thesemiconductor crystal along crystallographic planes. Cleaving has theadvantage over sawing or through wafer cutting with a laser in thatthere is no kerf, i.e. width of material lost due to the thickness ofthe blade or spot size of a cutting laser. Cleaving also is used inproducing highly smooth and flat surfaces at either end of a laser barto act as reflective surfaces. Dicing with a saw or laser would leaverough surfaces that would absorb or scatter light and result in poorperformance as a laser. Moreover, in substrate orientations with lowin-plane symmetry (e.g. non-polar and semi-polar orientations of GaN)there is typically a preferential orientation for the laser ridge withrespect to the crystal structure of the device. Cleavage of thesubstrate is a catastrophic event, and cannot be localized to only partof a wafer; i.e. the crack formed during the cleaving will tend topropagate across the entire wafer. Cleaves, for either singulation orfacet formation, must be aligned with the laser diode ridges and otherpatterning to avoid cleaving a device in half.

Typically, laser diode wafers fabricated with cleaved facets are cleavedtwice. They are initially singulated into so-called laser bars whichconsist of many individual laser die side by side with the laser ridgesrunning perpendicular to the cleaved facets such that the cleaves thatform the bar also form the front and back facet of the laser cavities.The bars are then stacked one atop the other with cleaved facets facingout. Reflective and anti-reflective coatings as required by the laserdiode design are then deposited onto the front and back facets as agroup. In the case of several small area substrates bonded haphazardlyto a handle and processed in parallel with lithography aligned to eachindividual substrate, then one would need to debond and cleave eachsubstrate separately. This example is the method of bonding the ensembleof small area substrates to a handle wafer while having thecrystallographic directions of the individual substrates aligned aswells as having the substrates placed on the handle wafer in such a waythat optimizes utilization of the substrate surface while preserving thetranslational symmetry of the mask pattern between substrates. Thisallows all processing steps to be carried out on the ensemble ofsubstrates in parallel; including cleaving into bars and bar-levelprocessing through to die singulation. Further details of the presenttechniques can be found throughout the present specification, and moreparticularly below.

FIG. 1: Illustration of a handle wafer 303 with several small areasubstrates 300 bonded to it. Layers of bonding media 301 and 302 areoverlaid on the bonding surfaces of the wafers and handle.

FIG. 2: Illustration of a handle wafer 303 bonded to small areasubstrates 300 using a bonding media 302. Alignment marks 306 arepatterned into the bonding media overlaid on the handle wafer.

FIG. 3: Illustration of a handle wafer 303 bonded to small areasubstrates 300 using a bonding media 302 that has been deposited ontothe handle wafer in a pattern. The pattern allows for quick alignment ofthe small area wafers to the handle.

FIG. 4: Illustration of a handle wafer 303 bonded to several small areasubstrates 300. Alignment marks 307 were positioned on the handle waferto allow for precise placement of small area substrates. Each small areawafer has an edge exclusion region with a border 309. The reticleexposure area 308A is chosen such that a whole number of exposures fullycover the central good region of the small area wafers. The spacingbetween small area wafers is chosen such that a whole number ofexposures 308B span the distance between the edges of the exclusionregion of adjacent small area substrates.

FIG. 5: Illustration of azimuthal (i.e. in-plane angular) alignment ofmany small area wafers. (A) shows wafers with a high degree of azimuthalalignment. (B) shows wafers bonded with a low degree of azimuthalalignment. In the case of (B) in order for laser ridges to be alignedparallel to the [0001] in-plane projection the mask would have to bealigned to each wafer individually. The wafers in (B) would also not becleavable as an ensemble since any cleave initiated in the handle wouldresult in cleaves on the wrong facets in the substrates. These waferswould have to be debonded and cleaved individually.

FIG. 6: Illustration of cleaving of bonded wafers as an ensemble. Thehandle 303 is cleaved or sawed into a regular shape which will yieldcomposite bars of uniform length. The handle and small area wafers arethen cleaved perpendicular to the laser ridges. Cleaving may includeformation of guide or skip scribes on either or both the front or backof the handle or small area substrates. The bars are then stacked inpreparation for deposition of reflective or antireflective coatings onthe front and back facets 317 & 318.

FIG. 7: Illustration of bonding from examples structures. 10 mm×20 mmlaser diode device wafers are bonded to a handle wafer 303. Alignmentmarks 307 allow for precise placement of device wafers. The interfacebetween the central good area and the edge exclusion region is shown bythe dashed lines 309. The good area existing inside of the edgeexclusion region has a size of 8 mm×18 mm.

FIG. 8A: Laser diode device wafer 300 including GaN substrate layer 203,n-type cladding 200, light emitting layers 201 and p-type cladding 202.A gold bonding layer is deposited on the backside of the substratelayer. The device wafer is then bonded to the first handle 303 via agold bonding layer 302.

FIG. 8B: Ridges, passivation layers and electrical contacts have beenfabricated into the epitaxial layers of the laser device wafer 300. Thetop of the epitaxial layers are then bonded to the second handle 305using the second bonding medium 304, which in this case is an adhesivewax. The first handle is removed and the GaN substrate is thinned.

FIG. 8C: Laser device wafer, bonded to second handle. Backsideelectrical contact layers 313 overlaid on backside of thinned substratelayer. The device wafer is subsequently debonded from the second handleand cleaved into bars.

FIG. 9: Schematic diagram of semipolar laser diode with the cavityaligned in the projection of c-direction with cleaved or etched mirrorsaccording to an example of the present invention.

FIG. 10: Schematic cross-section of ridge laser diode according to anexample of the present invention.

These aforementioned devices include a gallium and nitrogen containingsubstrate (e.g., GaN) comprising a surface region oriented in either asemipolar or non-polar configuration, but can be others. The device alsohas a gallium and nitrogen containing material comprising InGaNoverlying the surface region. In a specific embodiment, the presentlaser device can be employed in either a semipolar or non-polar galliumcontaining substrate, as described below. As used herein, the term“substrate” can mean the bulk substrate or can include overlying growthstructures such as a gallium and nitrogen containing epitaxial region,or functional regions such as n-type GaN, combinations, and the like. Wehave also explored epitaxial growth and cleave properties on semipolarcrystal planes oriented between the nonpolar m-plane and the polarc-plane. In particular, we have grown on the {30-31} and {20-21}families of crystal planes. We have achieved promising epitaxystructures and cleaves that will create a path to efficient laser diodesoperating at wavelengths from about 400 nm to green, e.g., 500 nm to 540nm. These results include bright blue epitaxy in the 450 nm range,bright green epitaxy in the 520 nm range, and smooth cleave planesorthogonal to the projection of the c-direction. It is desirable toalign the laser cavities parallel to the projection of the c-directionfor maximum gain on this family of crystal planes.

In a specific embodiment, the gallium nitride substrate member is a bulkGaN substrate characterized by having a semipolar or non-polarcrystalline surface region, but can be others. In a specific embodiment,the bulk nitride GaN substrate comprises nitrogen and has a surfacedislocation density between about 10E5 cm⁻² and about 10E7 cm⁻² or below10E5 cm⁻². The nitride crystal or wafer may compriseAl_(x)In_(y)Ga_(1-x-y)N, where 0≦x, y, x+y≦1. In one specificembodiment, the nitride crystal comprises GaN. In one or moreembodiments, the GaN substrate has threading dislocations, at aconcentration between about 10E5 cm⁻² and about 10E8 cm⁻², in adirection that is substantially orthogonal or oblique with respect tothe surface. As a consequence of the orthogonal or oblique orientationof the dislocations, the surface dislocation density is between about10E5 cm⁻² and about 10E7 cm⁻² or below about 10E5 cm⁻². In a specificembodiment, the device can be fabricated on a slightly off-cut semipolarsubstrate as described in U.S. Ser. No. 12/749,466 filed Mar. 29, 2010,which claims priority to U.S. Provisional No. 61/164,409 filed Mar. 28,2009, commonly assigned, and hereby incorporated by reference herein.

The substrate typically is provided with one or more of the followingepitaxially grown elements, but is not limiting:

-   -   an n-GaN cladding region with a thickness of 50 nm to about 6000        nm with a Si or oxygen doping level of about 5E16 cm⁻³ to 1E19        cm⁻³    -   an InGaN region of a high indium content and/or thick InGaN        layer(s) or Super SCH region;    -   a higher bandgap strain control region overlying the InGaN        region;    -   optionally, an SCH region overlying the InGaN region;    -   multiple quantum well active region layers comprised of three to        five or four to six 3.0-5.5.0 nm InGaN quantum wells separated        by 1.5-10.0 nm GaN barriers    -   optionally, a p-side SCH layer comprised of InGaN with molar a        fraction of indium of between 1% and 10% and a thickness from 15        nm to 100 nm    -   an electron blocking layer comprised of AlGaN with molar        fraction of aluminum of between 5% and 20% and thickness from 10        nm to 15 nm and doped with Mg.    -   a p-GaN cladding layer with a thickness from 400 nm to 1000 nm        with Mg doping level of 5E17 cm⁻³ to 1E19 cm⁻³    -   a p++-GaN contact layer with a thickness from 20 nm to 40 nm        with Mg doping level of 1E20 cm⁻³ to 1E21 cm⁻³

Typically each of these regions is formed using at least an epitaxialdeposition technique of metal organic chemical vapor deposition (MOCVD),molecular beam epitaxy (MBE), or other epitaxial growth techniquessuitable for GaN growth. The active region can include one to twentyquantum well regions according to one or more embodiments. As an examplefollowing deposition of the n-type Al_(u)In_(v)Ga_(1-u-v)N layer for apredetermined period of time, so as to achieve a predeterminedthickness, an active layer is deposited. The active layer may comprise asingle quantum well or a multiple quantum well, with 2-10 quantum wells.The quantum wells may comprise InGaN wells and GaN barrier layers. Inother embodiments, the well layers and barrier layers compriseAl_(w)In_(x)Ga_(1-w-x)N and Al_(y)In_(z)Ga_(1-y-z)N, respectively, where0≦w, x, y, z, w+x, y+z≦1, where w<u, y and/or x>v, z so that the bandgapof the well layer(s) is less than that of the barrier layer(s) and then-type layer. The well layers and barrier layers may each have athickness between about 1 nm and about 15 nm. In another embodiment, theactive layer comprises a double heterostructure, with an InGaN orAlwInxGa1-w-xN layer about 10 nm to 100 nm thick surrounded by GaN orAl_(y)In_(z)Ga_(1-y-z)N layers, where w<u, y and/or x>v, z. Thecomposition and structure of the active layer are chosen to providelight emission at a preselected wavelength. The active layer may be leftundoped (or unintentionally doped) or may be doped n-type or p-type.

The active region can also include an electron blocking region, and aseparate confinement heterostructure. In some embodiments, an electronblocking layer is preferably deposited. The electron-blocking layer maycomprise Al_(s)In_(t)Ga_(1-s-t)N, where 0≦s, t, s+t≦1, with a higherbandgap than the active layer, and may be doped p-type or the electronblocking layer comprises an AlGaN/GaN super-lattice structure,comprising alternating layers of AlGaN and GaN. Alternatively, there maybe no electron blocking layer. As noted, the p-type gallium nitridestructure, is deposited above the electron blocking layer and activelayer(s). The p-type layer may be doped with Mg, to a level betweenabout 10E16 cm-3 and 10E22 cm-3, and may have a thickness between about5 nm and about 1000 nm. The outermost 1-50 nm of the p-type layer may bedoped more heavily than the rest of the layer, so as to enable animproved electrical contact.

FIG. 10 is a simplified schematic cross-sectional diagram illustrating alaser diode structure according to embodiments of the presentdisclosure. This diagram is merely an example, which should not undulylimit the scope of the claims herein. One of ordinary skill in the artwould recognize other variations, modifications, and alternatives. Asshown, the laser device includes gallium nitride substrate 203, whichhas an underlying n-type metal back contact region 201. In anembodiment, the metal back contact region is made of a suitable materialsuch as those noted below and others. Further details of the contactregion can be found throughout the present specification and moreparticularly below.

In an embodiment, the device also has an overlying n-type galliumnitride layer 205, an active region 207, and an overlying p-type galliumnitride layer structured as a laser stripe region 211. Additionally, thedevice also includes an n-side separate confinement hetereostructure(SCH) 206, p-side guiding layer or SCH 208, p-AlGaN EBL 209, among otherfeatures. In an embodiment, the device also has a p++ type galliumnitride material 213 to form a contact region. In an embodiment, the p++type contact region has a suitable thickness and may range from about 10nm 50 nm, or other thicknesses. In an embodiment, the doping level canbe higher than the p-type cladding region and/or bulk region. In anembodiment, the p++ type region has doping concentration ranging fromabout 10¹⁹ to 10²¹ Mg/cm³, and others. The p++ type region preferablycauses tunneling between the semiconductor region and overlying metalcontact region. In an embodiment, each of these regions is formed usingat least an epitaxial deposition technique of metal organic chemicalvapor deposition (MOCVD), molecular beam epitaxy (MBE), or otherepitaxial growth techniques suitable for GaN growth. In an embodiment,the epitaxial layer is a high quality epitaxial layer overlying then-type gallium nitride layer. In some embodiments the high quality layeris doped, for example, with Si or O to form n-type material, with adopant concentration between about 10¹⁶ cm⁻³ and 10²⁰ cm⁻³.

The device has a laser stripe region formed overlying a portion of theoff-cut crystalline orientation surface region. As example, FIG. 9 is asimplified schematic diagram of semipolar laser diode with the cavityaligned in the projection of c-direction with cleaved or etched mirrors.The laser stripe region is characterized by a cavity orientationsubstantially in a projection of a c-direction, which is substantiallynormal to an a-direction. The laser strip region has a first end 107 anda second end 109 and is formed on a projection of a c-direction on a{20-21} gallium and nitrogen containing substrate having a pair ofcleaved mirror structures, which face each other. The first cleavedfacet comprises a reflective coating and the second cleaved facetcomprises no coating, an antireflective coating, or exposes gallium andnitrogen containing material. The first cleaved facet is substantiallyparallel with the second cleaved facet. The first and second cleavedfacets are provided by a scribing and breaking process according to anembodiment or alternatively by etching techniques using etchingtechnologies such as reactive ion etching (RIE), inductively coupledplasma etching (ICP), or chemical assisted ion beam etching (CAIBE), orother method. The first and second mirror surfaces each comprise areflective coating. The coating is selected from silicon dioxide,hafnia, and titania, tantalum pentoxide, zirconia, includingcombinations, and the like. Depending upon the design, the mirrorsurfaces can also comprise an anti-reflective coating.

In a specific embodiment, the method of facet formation includessubjecting the substrates to a laser for pattern formation. In apreferred embodiment, the pattern is configured for the formation of apair of facets for one or more ridge lasers. In a preferred embodiment,the pair of facets face each other and are in parallel alignment witheach other. In a preferred embodiment, the method uses a UV (355 nm)laser to scribe the laser bars. In a specific embodiment, the laser isconfigured on a system, which allows for accurate scribe linesconfigured in one or more different patterns and profiles. In one ormore embodiments, the laser scribing can be performed on the back-side,front-side, or both depending upon the application. Of course, there canbe other variations, modifications, and alternatives.

In a specific embodiment, the method uses backside laser scribing or thelike. With backside laser scribing, the method preferably forms acontinuous line laser scribe that is perpendicular to the laser bars onthe backside of the GaN substrate. In a specific embodiment, the laserscribe is generally 15-20 um deep or other suitable depth. Preferably,backside scribing can be advantageous. That is, the laser scribe processdoes not depend on the pitch of the laser bars or other like pattern.Accordingly, backside laser scribing can lead to a higher density oflaser bars on each substrate according to a preferred embodiment. In aspecific embodiment, backside laser scribing, however, may lead toresidue from the tape on one or more of the facets. In a specificembodiment, backside laser scribe often requires that the substratesface down on the tape. With front-side laser scribing, the backside ofthe substrate is in contact with the tape. Of course, there can be othervariations, modifications, and alternatives.

Laser scribe Pattern: The pitch of the laser mask is about 200 um, butcan be others. The method uses a 170 um scribe with a 30 um dash for the200 um pitch. In a preferred embodiment, the scribe length is maximizedor increased while maintaining the heat affected zone of the laser awayfrom the laser ridge, which is sensitive to heat.

Laser scribe Profile: A saw tooth profile generally produces minimalfacet roughness. It is believed that the saw tooth profile shape createsa very high stress concentration in the material, which causes thecleave to propagate much easier and/or more efficiently.

In a specific embodiment, the method of facet formation includessubjecting the substrates to mechanical scribing for pattern formation.In a preferred embodiment, the pattern is configured for the formationof a pair of facets for one or more ridge lasers. In a preferredembodiment, the pair of facets face each other and are in parallelalignment with each other. In a preferred embodiment, the method uses adiamond tipped scribe to physically scribe the laser bars, though aswould be obvious to anyone learned in the art a scribe tipped with anymaterial harder than GaN would be adequate. In a specific embodiment,the laser is configured on a system, which allows for accurate scribelines configured in one or more different patterns and profiles. In oneor more embodiments, the mechanical scribing can be performed on theback-side, front-side, or both depending upon the application. Ofcourse, there can be other variations, modifications, and alternatives.

In a specific embodiment, the method uses backside scribing or the like.With backside mechanical scribing, the method preferably forms acontinuous line scribe that is perpendicular to the laser bars on thebackside of the GaN substrate. In a specific embodiment, the laserscribe is generally 15-20 um deep or other suitable depth. Preferably,backside scribing can be advantageous. That is, the mechanical scribeprocess does not depend on the pitch of the laser bars or other likepattern. Accordingly, backside scribing can lead to a higher density oflaser bars on each substrate according to a preferred embodiment. In aspecific embodiment, backside mechanical scribing, however, may lead toresidue from the tape on one or more of the facets. In a specificembodiment, backside mechanical scribe often requires that thesubstrates face down on the tape. With front-side mechanical scribing,the backside of the substrate is in contact with the tape. Of course,there can be other variations, modifications, and alternatives.

Etch techniques such as chemical assisted ion beam etching (CAIBE),inductively coupled plasma (ICP) etching, or reactive ion etching (RIE)can result in smooth and vertical etched sidewall regions, which couldserve as facets in etched facet laser diodes. In the etched facetprocess a masking layer is deposited and patterned on the surface of thewafer. The etch mask layer could be comprised of dielectrics such assilicon dioxide (SiO2), silicon nitride (SixNy), a combination thereofor other dielectric materials. Further, the mask layer could becomprised of metal layers such as Ni or Cr, but could be comprised ofmetal combination stacks or stacks comprising metal and dielectrics. Inanother approach, photoresist masks can be used either alone or incombination with dielectrics and/or metals. The etch mask layer ispatterned using conventional photolithography and etch steps. Thealignment lithography could be performed with a contact aligner orstepper aligner. Such lithographically defined mirrors provide a highlevel of control to the design engineer. After patterning of thephotoresist mask on top of the etch mask is complete, the patterns inthen transferred to the etch mask using a wet etch or dry etchtechnique. Finally, the facet pattern is then etched into the waferusing a dry etching technique selected from CAIBE, ICP, RIE and/or othertechniques. The etched facet surfaces must be highly vertical of betweenabout 87 and 93 degrees or between about 89 and 91 degrees from thesurface plane of the wafer. The etched facet surface region must be verysmooth with root mean square roughness values of less than 50 nm, 20 nm,5 nm, or 1 nm. Lastly, the etched must be substantially free fromdamage, which could act as nonradiative recombination centers and hencereduce the COMD threshold. CAIBE is known to provide very smooth and lowdamage sidewalls due to the chemical nature of the etch, while it canprovide highly vertical etches due to the ability to tilt the waferstage to compensate for any inherent angle in etch.

The laser stripe is characterized by a length and width. The lengthranges from about 50 microns to about 3000 microns, but is preferablybetween 10 microns and 400 microns, between about 400 microns and 800microns, or about 800 microns and 1600 microns, but could be others. Thestripe also has a width ranging from about 0.5 microns to about 50microns, but is preferably between 0.8 microns and 2.5 microns forsingle lateral mode operation or between 2.5 um and 35 um formulti-lateral mode operation, but can be other dimensions. In a specificembodiment, the present device has a width ranging from about 0.5microns to about 1.5 microns, a width ranging from about 1.5 microns toabout 3.0 microns, a width ranging from 3.0 microns to about 35 microns,and others. In a specific embodiment, the width is substantiallyconstant in dimension, although there may be slight variations. Thewidth and length are often formed using a masking and etching process,which are commonly used in the art.

The laser stripe is provided by an etching process selected from dryetching or wet etching. The device also has an overlying dielectricregion, which exposes a p-type contact region. Overlying the contactregion is a contact material, which may be metal or a conductive oxideor a combination thereof. The p-type electrical contact may be depositedby thermal evaporation, electron beam evaporation, electroplating,sputtering, or another suitable technique. Overlying the polished regionof the substrate is a second contact material, which may be metal or aconductive oxide or a combination thereof and which comprises the n-typeelectrical contact. The n-type electrical contact may be deposited bythermal evaporation, electron beam evaporation, electroplating,sputtering, or another suitable technique.

Conventional semiconductor fabrication based on lithographic processesenjoy an economy of scale in that fabrication costs are typicallyindependent of wafer size. Indeed, per wafer costs in terms of time andprocessing steps may be higher for smaller wafers as special jigs andfixtures may be need to provide a safe means of processing small waferson equipment designed for much larger wafers. It would be advantageousto be able to process many small wafers in parallel such that the costper fabrication step is shared by many wafers, lowering the per devicecost of fabrication. One might imagine that one could simply bond manywafers to a handle wafer of the correct dimensions, however this wouldignore several aspects of laser diode fabrication that require a specialmethodology for carrying out the bonding and processing. These problemsinclude:

Alignment of lithography with both the crystalstructure of the smallsubstrates such that ridges and facets are properly oriented for highestgain and lowest loss;

Alignment of small substrates with the lithographic pattern such thatoverlap of laser dies with the edge exclusion region of each small waferis minimized so as to maximize device yield.

This invention describes a method for overcoming these issues at allsteps in the laser diode fabrication process. This method includes thesteps of:

-   -   Providing aligning features on the handle wafer such that the        small gallium and nitrogen containing wafers can be bonded at        specified locations on the handle that allow for optimized yield        of devices within the area of the small gallium and nitrogen        containing wafers that is not part of the edge exclusion zone.    -   Providing aligning features on the handle wafer such that small        gallium and nitrogen wafers can be bonded with a reference        crystallographic direction to a reference direction on the        handle wafer.    -   Determining the orientation of a reference crystal direction for        each small gallium and nitrogen wafer;    -   Aligning the small gallium and nitrogen wafers to a reference        direction on the first handle wafer such that the reference        crystal direction for all small gallium and nitrogen wafers        bonded to a single handle wafer are aligned;    -   Bonding each small gallium and nitrogen wafer to the handle        either sequentially or via a two-step process of wafer placement        and then bonding of all small gallium and nitrogen wafers        simultaneously.

The method may include the subsequent steps of:

-   -   Processing of the top-side-side features of the laser devices on        the small gallium nitrogen wafers.    -   Bonding the small gallium and nitrogen wafers and their handle        as an ensemble to a second handle wafer using a second bonding        medium.    -   Removal of the first handle and first bonding medium.    -   Processing of the backside features of the devices on the small        gallium and nitrogen wafers.    -   Bonding the small gallium and nitrogen wafers and their handle        as an ensemble to a third handle wafer using a third bonding        medium.    -   Removal of the second handle and second bonding medium.    -   Cleaving of the first, second or third handle to form so called        bars of laser devices, where the cleaving into bars also forms        the first and second faceted mirrors of the laser cavities.    -   Formation of the laser facets using an etching process selected        from chemical assisted ion beam etching, inductively coupled        plasma etching, or reactive ion etching.

Handle wafers can be composed of GaN, AN, Al₂O₃, Si, Ge, SiC, quartz,silicate containing glasses, GaAs, InP, GaP, tungsten, molybdenum,steel, copper, aluminum and gold among others. In a preferred embodimenthandle wafers used in process steps where the handle will be cleavedwill be single crystal wafers, though polycrystalline, amorphous andcomposite handle wafers composed of more than one material are useablein this method.

In a preferred embodiment the bonding media will be deposited either onthe handle wafer or the bonded surface of the small wafers or both. In apreferred embodiment, functional device layers can be overlaid on thesubstrate wafer before application of the bonding media. For example,metallic electrical contact layers may be evaporated onto the p-typesurface of the laser device wafer. A thick gold bonding layer is thenoverlaid using evaporation deposition over the electrical contactlayers. Such functional layers may include but are not limited to:dielectric passivation, electrical contact layers, lateral opticalconfinement layers, vertical optical confinement layers, currentspreading layers and current aperture layers.

Bonding media and techniques applicable to this invention includemetal-metal thermocompressive bonding (e.g. Au—Au bonding), organicwaxes and polymers (e.g. crystalbond, polymethylmethacrylate [PMMA],photo-resist, benzocyclobutene, etc.), spin-on-glass and metal soldersamong others. For example, in one embodiment the handle wafer and thebonded surface of the small wafers are coated in a thin layer (0.05-5microns) of gold either by evaporation, sputtering or electroplating.Other metals can be included in the metal layers to promote adhesion;for example layers of Ti may be included. The small wafers and thehandle are bonded together gold layer to gold layer at temperaturesabove 150 C and at pressures greater than 15 pounds per square inch. Inanother embodiment, the handle wafers is coated in an organic wax withlow melting point (e.g. Crystalbond 509). The handle can be coatedeither by melting of solid wax or by spin on of wax dissolved in asolvent. The small area wafers are then aligned to their final positionbefore being bought into contact with the wax. The wax is melted byelevation of the entire handle wafer or local heating around the smallwafer and the small wafer. Small amounts of pressure may be used tobring wax into intimate contact with the small wafer.

In a preferred embodiment the first handle will be patterned withfeatures that allow for proper angular and lateral alignment of thesmall wafers during the initial bonding process. The second and thirdhandle need not be patterned as the small wafers will be transferred asan ensemble while still bonded and held rigidly to a handle wafer. Thealignment features may be produced by patterning the bonding mediadeposited on the handle wafer, etching features into the handle,deposition of a material, e.g. metal, on the handle wafer or the bondingmedia. If the handle is transparent to visible or non-visiblewavelengths of light then the patterning for alignment can be providedon the opposite side of the handle from the bonded small wafers.

Alignment features and proper alignment of smalla area substrates toeach other are critical in two regards. The first is in imbodimentswhere a handle wafer is cleaved and the cleave propagates into one ormore small wafers bonded to the handle. In order for the cleave topropagate into the small wafers and form a facet that is not highlyscattering, and therefore lossy, the cleavage plain of the handle mustbe aligned sufficiently close to the orientation of a cleavage plane inthe small area substrate. If the two cleavage planes deviate then thehandle may dominate the cleave direction, forcing the cleave in thesmall area wafer to be composed of a vicinal surface which deviates froma cleavage plane and has a microstructure dominated by microfacets or isotherwise neither planar nor smooth. The second advantage is in the caseof forming ridges that maximize gain. As mentioned above, it has beenfound that the gain in non-polar and semi-polar GaN laser diode devicesis dependent on the crystallographic orientation of the laser ridge. Ina process where multiple small area wafers are lithographicallypatterned with ridge features using a single alignment, it is necessarythat the small area wafers be bonded to the handle wafer withsufficiently close crystallographic alignment among the plurality ofsmall area wafers that the fabricated ridges are patterned to withinsome small deviation of the optimal crystallographic orientation on allof the small area wafers. In a particular embodiment, where the mirrorfacets on either end of the laser ridges are formed by an etch processrather than a cleave the tolerance for the alignment of the small areawafers is somewhat larger than for cleaved facets as the dependence ofthe device gain on orientation is somewhat less than the dependence ofcleave quality on orientation. It is therefore advantageous to combineetched facets with crystallographically aligned small area wafers in anyprocessing of an ensemble of small area wafers bonded to a handle. In apreferred embodiment, the crystal structures of the small areasubstrates are aligned to within 10 degrees or less of each other in theplane of the bonded interface. In the most preferred embodiment, thecrystal structures of the small area substrates are aligned to within 1degree or less of each other in the plane of the bonded interface.

In a preferred embodiment the crystal directions of the small waferswill be determined by the wafer manufacturer using x-ray diffraction.The wafers will then be shaped with a so-called orienting flat, a notchor any other geometric feature of the wafer which is aligned with areference direction in the crystal to within some high tolerance (e.g.aligned to within 1 degree of the true crystal direction). In anotherembodiment the reference crystal direction in the small wafers will bedetermined by X-ray measurements of the individual small wafers. Thereference direction can be indicated on the wafer by patterning thewafer with one or a combination of a lithographically defined pattern,and ink mark, tape, a mechanical scribe or a scribe formed with a laser.In another embodiment the reference crystal direction in the smallwafers will be determined by cleaving the edge of the wafer in adirection parallel to a known cleavage plane of the crystal.

In a preferred embodiment the small wafers will be aligned for bondingby using a die bonding machine providing alignment accuracy to withintolerances of less than 20 microns. A die bonder could include analigner/bonder system whereby a special jig is used in a contact alignerto align the small wafers to the handle and make the initial placementof the wafers and a dedicated bonding tool is used to create the finalbond. In a less preferred embodiment alignment will be achieved bymanipulating the small wafer by hands before introducing the wafer andhandle to the final bonding process.

Each of the small wafers will provide a central good region and an edgeexclusion region. A The edge exclusion region consists of that area nearthe edge of the wafer that is less uniform or otherwise of lesserquality than the material near the wafer center due to the presence ofthe wafer edge during epitaxy. The edge exclusion region also includesthe area near the wafer edge where the photoresist thickness is not thesame as for the bulk of the wafer surface; i.e. the so-calledphoto-resist edge bead. The edge bead is typically thicker than theresist layer over the majority of the wafer, and the difference inthickness will typically result in a difference in the quality oflithographic patterning for the material near the edge. If a portion ofa row of laser diode devices overlaps the edge exclusion region then allof those devices are likely to be defective. Maximizing yield of useabledevices requires alignment of the lithographic mask with the centralgood region such that a maximum number of devices are placed within thecentral good region.

In a preferred embodiment of the method a lithographic stepper will beused to pattern the wafers. The mask reticle size will be chosen suchthat the entirety of the central good region can be exposed using awhole number of exposures. The spacing between small area wafers will bechosen such that a whole number of exposures can be fit between theadjacent edges of the central good regions of adjacent small areawafers. In this way the lithography process can be aligned once to a keywafer and then exposures can be made automatically across many waferswith a maximum of devices patterned into the central good region of eachindividual wafer. In a less preferred embodiment of the method, acontact aligner is used to pattern the wafers. Here the mask is acontinuous array of laser ridges and patterns. The spacing betweenwafers will be chosen such that the registry between the laser patternsand the edges of the central good region on one wafer is preserved forall other wafers bonded to the same handle.

In a specific embodiment, the method of facet formation includessubjecting the substrates to a laser or mechanical scribe afterdebonding from the handle wafers for pattern formation. In thisembodiment, scribing and cleaving are consistent with the descriptiongiven above for typical fabrication on GaN substrates.

In a specific embodiment, the method of facet formation includessubjecting the handle wafers to a laser or mechanical scribe for patternformation with the small area wafers still bonded to the handle wafers.In a second embodiment, the handle wafers and the small area wafers willbe scribed. In a preferred embodiment, the pattern is configured for theformation of a pair of facets for one or more ridge lasers. In apreferred embodiment, the pair of facets face each other and are inparallel alignment with each other.

In a preferred embodiment, the method uses a UV (355 nm) laser to scribethe laser bars. In a specific embodiment, the laser is configured on asystem, which allows for accurate scribe lines configured in one or moredifferent patterns and profiles. In one or more embodiments, the laserscribing can be performed on the back-side, front-side, or both ofeither or both of the handle wafer and small area substrates dependingupon the application. Of course, there can be other variations,modifications, and alternatives. In a specific embodiment, the methoduses backside laser scribing or the like. With backside laser scribing,the method preferably forms a continuous line laser scribe that isperpendicular to the laser bars on the backside of the handle wafer. Ina specific embodiment, the laser scribe is generally 15-20 um deep orother suitable depth. Preferably, backside scribing can be advantageous.That is, the laser scribe process does not depend on the pitch of thelaser bars or other like pattern. Accordingly, backside laser scribingcan lead to a higher density of laser bars on each substrate accordingto a preferred embodiment. In a specific embodiment, backside laserscribing, however, may lead to residue from the tape on one or more ofthe facets. In a specific embodiment, backside laser scribe oftenrequires that the substrates face down on the tape. With front-sidelaser scribing, the backside of the handle is in contact with the tape.Of course, there can be other variations, modifications, andalternatives. In a specific embodiment a laser nick cleave can beemployed, where the laser scribe is produced only near the edge of thehandle wafer. The scribe then acts as a nucleation point for a crackwhich propagates along natural cleavage planes of the handle wafer.

In a second embodiment, the method uses a mechanical scribe stylustipped with diamond, SiC or some other acceptably hard material. In aspecific embodiment, the scribe stylus is configured on a system, whichallows for accurate scribe lines configured in one or more differentpatterns and profiles. In one or more embodiments, the laser scribingcan be performed on the back-side, front-side, or both of either or bothof the handle wafer and small area substrates depending upon theapplication. Of course, there can be other variations, modifications,and alternatives. In a specific embodiment, the method uses backsidescribing or the like. With backside scribing, the method preferablyforms a continuous line scribe that is perpendicular to the laser barson the backside of the handle wafer. In a specific embodiment, the laserscribe is generally 15-20 um deep or other suitable depth. Preferably,backside scribing can be advantageous. That is, the laser scribe processdoes not depend on the pitch of the laser bars or other like pattern.Accordingly, backside laser scribing can lead to a higher density oflaser bars on each substrate according to a preferred embodiment. In aspecific embodiment, backside scribing, however, may lead to residuefrom the tape on one or more of the facets. In a specific embodiment,backside scribing often requires that the substrates face down on thetape. With front-side scribing, the backside of the handle is in contactwith the tape. Of course, there can be other variations, modifications,and alternatives. In a specific embodiment and nick cleave can beemployed, where the scribe is produced only near the edge of the handlewafer. The scribe then acts as a nucleation point for a crack whichpropagates along natural cleavage planes of the handle wafer.

Example 1

Laser diode device structures are grown using MOCVD on nominally on-axis(10-10) oriented, rectangular GaN substrates with dimensions of 10 mm by20 mm, where the projection of the [0001] direction in the plane of theprimary surface of the substrates is aligned parallel to the 10 mm longedge and the in-plane [11-20] direction is parallel to the 20 mm longedge. The substrates are single side polished, with the non-epitaxialsides having an acid etched surface. The backsides of the substratewafers are lapped to a mirror finish. A 3 inch diameter single-crystal(100) oriented silicon first handle wafer is patterned with photoresistusing a lithographic process such that alignment marks are present onthe first handle wafer surface. The alignment marks are designed toprovide clear indication of the orientations of the in-plane <110>directions in the silicon wafer. A 250 nm thick gold bonding layer isthen deposited on the handle wafer and the back-side of the small areaGaN substrates using an e-beam evaporation process. The photoresist onthe handle wafer is then stripped, leaving negative images of thealignment marks in the gold film. The GaN substrates are then aligned tothe Si wafer using a die bonding machine.

The GaN wafers are aligned such that the in-plane projection of the[0001] direction of each GaN substrate is aligned to the same <110>direction to within 1 degree. The GaN wafers are bonded in a rectangulararray, with the long and short edges of the wafers aligned parallel tothe two displacement vectors of the array. In this case, the edgeexclusion region is 1 mm in width. The GaN wafers are placed and bondedas shown in FIG. 7 and FIG. 8A, with long and short edges of the GaNwafers parallel and with the gold bonding layers of both the firsthandle and the GaN wafers in contact. The stepper mask projected area is4 mm×9 mm, such that 4 exposures can cover the full area inside theboundary of the edge exlusion region. The GaN wafers are spaced with 2mm between long edges and 7 mm between short edges with tolerance of 30microns, such that one exposure with the mask will span the distancebetween good regions on adjacent GaN wafers. The initial bond is carriedout in the die bonder, with each GaN wafer bonded at greater than 300degrees Celsius immediately after alignment and placement. In someembodiments a subsequent bonding step is used where the ensemble of GaNwafers are held at temperatures above 300 degrees Celsius and atelevated pressures in order to strengthen the gold-gold bond.

The GaN wafer top-side processes are then carried out in order tofabricated laser ridges, layers of passivating dielectric, deposition ofmetal electrical contacts and deposition of metal bond pads forwire-bonding of the final laser diode die during packaging. At thispoint any front-side laser scribing required for facet cleaving ordie-singulation is carried out. Photo-resist is spun onto the entirecomposite wafer. Edge bead at the edges of the small GaN wafers isavoided by using projection lithography with a stepper. In processingsteps that might damage the bonding medium, for example in this casewere there a processing step involving gold etchant, then a protectivelayer of photoresist could be created using contact lithography aroundthe edge of each wafer to isolate the bonded interface from anychemicals or etch processes. Here, the same photoresist could be used toboth pattern the GaN wafers with projection lithography and protect thebonding medium using contact lithography.

The GaN wafers are then transferred to a second handle wafer forbackside processing as shown in FIG. 8B. A 3 inch diametersingle-crystal [100] oriented silicon second handle wafer is produced. Amixture of dissolved, commercially available adhesive wax (in this caseCrystalbond 509) is produced from dissolution of 1 part Crystalbond in 4parts acetone. This dissolved wax is then spun onto the second handlewafer at greater than 1000 RPM using a commercially available waferspinner as one would do for spinning on photoresist. The acetone is thenevaporated in a two-step process, first for 10 minutes are roomtemperature and then for 2 minutes at 80 degrees Celsius.

The first and second handles are then arranged using a jig such that theorienting flats are aligned and the crystallographic directions of thesmall area GaN wafers are aligned with the correct directions of thesecond handle. The unbonded surfaces of the GaN wafers are then broughtinto contact with the Crystalbond on the second handle. While undercontact the wafers are heated to 120-130 degrees Celsius to melt theCrystalbond and adhere the GaN wafers to the second handle.

The first handle is then removed using a lapping process. Once the firsthandle is fully removed the small area GaN wafers are thinned as anensemble, while bonded to the second handle, using a similar lappingprocess. The GaN wafers are thinned to approximately 100 microns inthickness. The GaN backside processing steps are then carried out inorder to form n-type electrical contacts as well as fabrication of anyback-side laser scribes required for the facet cleaving anddie-singulation processes. The resulting structure is similar to thatshown in FIG. 8C.

The small area GaN wafers are then debonded from the second handle,either mechanically after melting the wax adhesive, or chemically bydissolving the wax adhesive in solvent. After cleaning to remove any waxresidue, the wafers are cleaved into bars while at the same time formingthe front and back facet of the laser cavities. The bars are thenstacked and depending on the application reflective and antireflectivecoatings are deposited on the facets. The bars are then singulated usingcleaving into individual laser diode die.

Example 2

Laser diode device structures are grown using MOCVD on nominally on-axis(10-10) oriented, rectangular GaN substrates with dimensions of 10 mm by20 mm, where the projection of the [0001] direction in the plane of theprimary surface of the substrates is aligned parallel to the 10 mm longedge and the in-plane [11-20] direction is parallel to the 20 mm longedge. The substrates are single side polished, with the non-epitaxialsides having an acid etched surface. The GaN substrates are cleanedchemically with acids and solvents to remove any surface contamination,and then top-side, cladding and electrical-contact layers are overlaidon the epitaxial-side of the GaN substrates using a blanket e-beamdeposition process. After the contact layer deposition, a blanket 250 nmthick gold bond layer is overlaid on the contact layers. A 3 inchdiameter single-crystal (100) oriented GaAs first handle wafer ispatterned with photoresist using a lithographic process such thatalignment marks are present on the first handle wafer surface. Thealignment marks are designed to provide clear indication of theorientations of the in-plane <110> directions in the GaAs wafer. A 250nm thick gold bonding layer is then deposited on the handle wafer usingan e-beam evaporation process. The photoresist on the handle wafer isthen stripped, leaving negative images of the alignment marks in thegold film. The GaN substrates are then aligned to the Si wafer using adie bonding machine.

The GaN wafers are aligned such that the in-plane projection of the[0001] direction of each GaN substrate is aligned to the same <110>direction to within 1 degree. The GaN wafers are bonded in a rectangulararray, with the long and short edges of the wafers aligned parallel tothe two displacement vectors of the array. In this case, the edgeexclusion region is 1 mm in width. The GaN wafers are placed and bondedas shown in FIG. 7, with long and short edges of the GaN wafers paralleland with the gold bonding layers of both the first handle and the GaNwafers in contact. The stepper mask projected area is 4 mm×9 mm, suchthat 4 exposures can cover the full area inside the boundary of the edgeexlusion region. The GaN wafers are spaced with 2 mm between long edgesand 7 mm between short edges with tolerance of 30 microns, such that oneexposure with the mask will span the distance between good regions onadjacent GaN wafers. The initial bond is carried out in the die bonder,with each GaN wafer bonded at greater than 300 degrees Celsiusimmediately after alignment and placement. In some embodiments asubsequent bonding step is used where the ensemble of GaN wafers areheld at temperatures above 300 degrees Celsius and at elevated pressuresin order to strengthen the gold-gold bond.

The GaN wafer back-side processes are then carried out. The GaN wafersare thinned considerably using a one or more techniques of lapping,physical and chemical (wet or dry) etches. After GaN substrate thinning,laser structures are fabricated by the formation of laser ridges,overlaying of layers of passivating dielectric, deposition of metalelectrical contacts and deposition of metal bond pads for wire-bondingof the final laser diode die during packaging. Edge bead at the edges ofthe small GaN wafers is avoided by using projection lithography with astepper. In processing steps that might damage the bonding medium, forexample in this case were there a processing step involving goldetchant, then a protective layer of photoresist could be created usingcontact lithography around the edge of each wafer to isolate the bondedinterface from any chemicals or etch processes. Here, the samephotoresist could be used to both pattern the GaN wafers with projectionlithography and protect the bonding medium using contact lithography.The GaN wafers are then bonded to a second handle. An adhesive wax (e.g.Crystalbond 509) can be used. In this process alignment to the secondhandle is not important. The second handle need only support thecomposite wafer during thinning of the first handle.

Once bonded to the second handle wafer, the first handle is then thinnedusing a lapping process to a thickness of approximately 100 micrometers.The GaN wafers and first handle are then debonded from the secondhandle, either mechanically after melting the wax adhesive, orchemically by dissolving the wax adhesive in solvent. After cleaning toremove any wax residue, the first handle-GaN substrate composite waferis then cleaved into composite bars while at the same time forming thefront and back facets of the laser device cavities. This process isdetailed in FIG. 6. The first handle is cleaved (FIG. 6A) to form arectangular piece that bounds the thinned GaN wafers. The first handleis then cleaved (FIG. 6B) parallel to the handle [110] which is parallelto the GaN in-plane [11-20] direction. The cleave locations are chosento align with the previously patterned contact pads and laser deviceridges. The composite bars are then stacked and, depending on theapplication, reflective and anti-reflective coatings are applied to thefront and back facets. The bars are then singulated using cleaving intoindividual laser diode die.

Example 3

Laser diode device structures are grown using MOCVD on nominally on-axis(10-10) oriented, rectangular GaN substrates with dimensions of 10 mm by20 mm, where the projection of the [0001] direction in the plane of theprimary surface of the substrates is aligned parallel to the 10 mm longedge and the in-plane [11-20] direction is parallel to the 20 mm longedge. The substrates are single side polished, with the non-epitaxialsides having an acid etched surface. The GaN substrates are cleanedchemically with acids and solvents to remove any surface contamination,and then top-side, cladding and electrical-contact layers are overlaidon the epitaxial-side of the GaN substrates using a blanket e-beamdeposition process. After the contact layer deposition, a blanket 250 nmthick gold bond layer is overlaid on the contact layers. A 3 inchdiameter single-crystal (100) oriented GaAs first handle wafer ispatterned with photoresist using a lithographic process such thatalignment marks are present on the first handle wafer surface. Thealignment marks are designed to provide clear indication of theorientations of the in-plane <110> directions in the GaAs wafer. A 250nm thick gold bonding layer is then deposited on the handle wafer usingan e-beam evaporation process. The photoresist on the handle wafer isthen stripped, leaving negative images of the alignment marks in thegold film. The GaN substrates are then aligned to the Si wafer using adie bonding machine.

The GaN wafers are aligned such that the in-plane projection of the[0001] direction of each GaN substrate is aligned to the same <110>direction to within 5 degrees. The GaN wafers are bonded in arectangular array, with the long and short edges of the wafers alignedparallel to the two displacement vectors of the array. In this case, theedge exclusion region is 1 mm in width. The GaN wafers are placed andbonded as shown in FIG. 7, with long and short edges of the GaN wafersparallel and with the gold bonding layers of both the first handle andthe GaN wafers in contact. The stepper mask projected area is 4 mm×9 mm,such that 4 exposures can cover the full area inside the boundary of theedge exlusion region. The GaN wafers are spaced with 2 mm between longedges and 7 mm between short edges with tolerance of 30 microns, suchthat one exposure with the mask will span the distance between goodregions on adjacent GaN wafers. The initial bond is carried out in thedie bonder, with each GaN wafer bonded at greater than 300 degreesCelsius immediately after alignment and placement. In some embodiments asubsequent bonding step is used where the ensemble of GaN wafers areheld at temperatures above 300 degrees Celsius and at elevated pressuresin order to strengthen the gold-gold bond.

The GaN wafer back-side processes are then carried out. The GaN wafersare thinned considerably using a one or more techniques of lapping,physical and chemical (wet or dry) etches. After GaN substrate thinning,laser structures are fabricated by the formation of laser ridges,overlaying of layers of passivating dielectric, deposition of metalelectrical contacts and deposition of metal bond pads for wire-bondingof the final laser diode die during packaging. It is during thisbackside processing, after thinning, that the laser ridge facets areformed using a dry etch method such as reactive ion etching, inductivelycoupled plasma etching, chemically assisted ion beam etching or thelike. Reflective and anti-reflective coatings are deposited on the frontand back facets of the ridge if required by the particular application.Temporary protective layers, for example ones consisting of photoresist,may be applied to the etched facets to protect them from damage orcontamination during subsequent processing steps.

The GaN wafers are then bonded to a second handle. An adhesive wax (e.g.Crystalbond 509) can be used. In this process alignment to the secondhandle is not important. The second handle need only support thecomposite wafer during thinning of the first handle.

Once bonded to the second handle wafer, the first handle is then thinnedusing a lapping process to a thickness of approximately 100 micrometers.The GaN wafers and first handle are then debonded from the secondhandle, either mechanically after melting the wax adhesive, orchemically by dissolving the wax adhesive in solvent. After cleaning toremove any wax residue, the first handle-GaN substrate composite waferis then cleaved into composite bars in a process similar to thatdetailed in FIG. 6. The first handle is cleaved (FIG. 6A) to form arectangular piece that bounds the thinned GaN wafers. The first handleis then cleaved (FIG. 6B) parallel to the handle [110] which is parallelto the GaN in-plane [11-20] direction. The cleave locations are chosento align with the previously patterned contact pads and laser deviceridges, producing cleaves that run between the etched facets of thefirst and second ends of the laser ridges. The bars are then singulatedusing cleaving into individual laser diode die.

In an example, the present invention provides a method for manufacturinga laser diode device from a plurality of gallium and nitrogen containingsemiconductor substrates, e.g., GaN. Each of the gallium and nitrogencontaining semiconductor substrates (“substrates”) has a plurality ofepitaxially grown layers overlaying a top-side of each of thesubstrates. The method includes determining an orientation of areference crystal direction for each of the substrates. The methodincludes aligning at least one of the substrates to a spatial regionconfigured in a selected direction of a first handle substrate, whichhas a larger spatial region than a sum of a total backside region ofplurality of the substrates to be arranged in a tiled configurationoverlying the first handle substrate, such that the reference crystaldirection for the substrate is parallel to the spatial region in theselected direction within 10 degrees or less, although there can beother orientations. In an example, the method includes mating a backsideregion of the substrate, which has been aligned, to a portion of asurface region of the first handle substrate. In an example, the methodincludes bonding the substrate to portion of the surface region of thefirst handle substrate using a first bonding medium provided between thefirst handle substrate and the substrate while maintaining the alignmentbetween reference crystal orientation and the selected direction of thefirst handle substrate. In an example, the method includes repeating thealigning, mating, and bonding for all of the other plurality ofsubstrates to form an array of substrates spatially disposed on thesurface region of the first handle substrate in the tiled arrangement.

In other examples, the reference crystal direction for each of thesubstrates is substantially parallel to within 5 degrees or less,parallel to within 3 degrees or less, or parallel to within 1 degree orless to the spatial region configured in the selected direction. In anexample, the reference crystal direction orientation is provided bycleaving the substrate to expose the reference crystal direction, isprovided by X-ray diffraction, or is provided by an orienting flat orotherwise from a determined shape of a portion of the substrate or othersuitable techniques.

In an example, the first handle substrate is patterned with one or morealignment marks or discontinuous regions of bonding media configured toalign the spatial region to each of the substrates. In an example, afterbonding each of the substrates with the first handle substrate, themethod processing each of the substrates, concurrently, by formingridges or some other means of inducing lateral optical mode confinementto form a laser stripe. In an example, the method includes after bondingeach of the substrates with the first handle substrate, processing eachof the substrates, concurrently, by forming dielectric passivationlayers. In an example, after bonding each of the substrates with thefirst handle substrate, the method includes processing each of thesubstrates, concurrently, by forming metal contacts and/or forming metalbond pads to the p-type and/or n-type gallium and nitrogen containinglayers. In an example, after bonding each of the substrates with thefirst handle substrate, the method includes processing each of thesubstrates, concurrently, by thinning the gallium and nitrogencontaining substrates via lapping or chemical etching. In otherexamples, any of the above combinations, and variations can be included.By way of the concurrent processing, efficiency and consistency isachieved.

In an example, the method further makes use of a second handlesubstrate, as well as others. In an example, the method comprisesbonding a second handle substrate using a second bonding medium to anupper region of each of the substrates to sandwich each of thesubstrates between the first handle substrate and the second handlesubstrate. The method includes bonding a second handle substrate using asecond bonding medium to an upper region of each of the substrates tosandwich each of the substrates between the first handle substrate andthe second handle substrate; and removing the first handle substratefrom each of the substrates while the second handle substrate remainsattached to each of the substrates; wherein removing the first handlesubstrate is selected from a process including one of laser lift-off, amechanical grinding or lapping, a chemical etching of the first handlesubstrate or a chemical etching or dissolution of the first bondingmedium provided between the first handle substrate and each of thesubstrates.

In an example, the method includes thinning a backside region of each ofthe substrates using any combination of a mechanical lapping andpolishing, chemical etching and physical etching, or other process. Inan example, the method includes bonding a second handle substrate usinga second bonding medium to an upper region of each of the substrates tosandwich each of the substrates between the first handle substrate andthe second handle substrate; and processing each of the exposed backsideregions of each of the substrates, while being attached to the secondhandle substrate, to one or more processes for at least one of metalcontacts, bond pads and/or dielectric passivation layers.

In an example, the method includes bonding a second handle substrateusing a second bonding medium to an upper region of each of thesubstrates to sandwich each of the substrates between the first handlesubstrate and the second handle substrate; and removing each of thesubstrates and forming at least a pair of cleaved regions to form a pairof facets, which are opposite of each other, using a cleaving process oneach of the substrates. In an example, the method includes bonding asecond handle substrate using a second bonding medium to an upper regionof each of the substrates to sandwich each of the substrates between thefirst handle substrate and the second handle substrate; and forming atleast a pair of cleaved region to form a pair of facets, which areopposite of each other, using a cleaving process while a portion of thesecond handle substrate remains attached to a laser diode bar.

In an example, the method includes after bonding each of the substrateswith the first handle substrate, processing each of the substrates,concurrently, by forming a thickness of dielectric passivation materialoverlying each of the substrates, and further comprising bonding each ofthe substrates to a third handle substrate using a third bonding mediumwith a third bonding medium located between the third handle wafer andthe substrates. In an example, the method includes bonding a secondhandle substrate using a second bonding medium to an upper region ofeach of the substrates to sandwich each of the substrates between thefirst handle substrate and the second handle substrate; and forming atleast a pair of cleaved region to form a pair of facets, which areopposite of each other, using a cleaving process while a portion of thesecond handle substrate remains attached to a laser diode bar; andthereafter removing the second handle substrate using at least one of alaser lift-off, mechanical grinding or lapping, chemical etching of thesecond handle substrate or chemical etching or dissolution of the secondbonding medium provided on the second handle substrate.

In an example, the method includes bonding each of the substrates to athird handle substrate; and forming a pair of cleaved region to formfacets, which are opposite of each other by cleaving the third handlesubstrate to yield a composite laser diode bar comprising the thirdhandle substrate portion bonded to one or more arrays of laser diodedevices. The method includes forming a pair of facets, which areopposite of each other, by an etching process selected from at least oneof reactive ion etching (RIE), chemical assisted ion beam etching(CAIBE), or inductively coupled plasma etching (ICP).

In an example, the present invention includes a method for manufacturinga laser diode device from a plurality of gallium and nitrogen containingsemiconductor substrates. Each of the gallium and nitrogen containingsemiconductor substrates (“substrates”) has a plurality of epitaxiallygrown layers overlaying a top-side of each of the substrates. The methodincludes determining an orientation of a reference crystal direction foreach of the substrates; and aligning at least one of the substrates to aspatial region configured in a selected direction of a first handlesubstrate, having a larger spatial region than a sum of a total backsideregion of plurality of the substrates, such that the reference crystaldirection for the substrate is parallel to the spatial region in theselected direction within 15 degrees or less, although there can bevariations. The method includes mating a backside region of thesubstrates, which has been aligned, to a portion of a surface region ofthe first handle substrate. The method includes bonding the substrate toportion of the surface region of the first handle substrate using afirst bonding medium provided between the first handle substrate and thesubstrate while maintaining the alignment between reference crystalorientation and the selected direction of the first handle substrate.The method includes repeating the aligning, mating, and bonding for allof the other plurality of substrates to form an array of substratesspatially disposed on the surface region of the first handle substrate.The method includes forming at least a pair of facets, which areopposite of each other, on each of the substrates using an etchingprocess selected from at least one of reactive ion etching (RIE),chemical assisted ion beam etching (CAIBE), or inductively coupledplasma etching (ICP).

In an example, the present invention provides a gallium and nitrogencontaining multilayered structure. The structure has a plurality ofgallium and nitrogen containing semiconductor substrates, each of thegallium and nitrogen containing semiconductor substrates (“substrates”)having a plurality of epitaxially grown layers overlaying a top-side ofeach of the substrates. The structure has an orientation of a referencecrystal direction for each of the substrates. The structure has a firsthandle substrate coupled to each of the substrates such that each of thesubstrates is aligned to a spatial region configured in a selecteddirection of the first handle substrate, which has a larger spatialregion than a sum of a total backside region of plurality of thesubstrates to be arranged in a tiled configuration overlying the firsthandle substrate. The reference crystal direction for each of thesubstrates is parallel to the spatial region in the selected directionwithin 10 degrees or less. The structure has a first bonding mediumprovided between the first handle substrate and each of the substratewhile maintaining the alignment between reference crystal orientationand the selected direction of the first handle substrate; and aprocessed region formed overlying each of the substrates configuredconcurrently while being bonded to the first handle substrate. Dependingupon the embodiment, the processed region can include any combination ofthe aforementioned processing steps and/or steps.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

What is claimed is:
 1. A gallium and nitrogen containing multilayeredstructure comprising: a plurality of gallium and nitrogen containingsemiconductor substrates, each of the gallium and nitrogen containingsemiconductor substrates (“substrates”) having a plurality ofepitaxially grown layers overlaying a top-side of each of thesubstrates; an orientation of a reference crystal direction for each ofthe substrates; a first handle substrate coupled to each of thesubstrates such that each of the substrates is aligned to a spatialregion configured in a selected direction of the first handle substrate,the first handle substrate having a larger spatial region than a sum ofa total backside region of plurality of the substrates to be arranged ina tiled configuration overlying the first handle substrate, thereference crystal direction for each of the substrates is parallel tothe spatial region in the selected direction within 10 degrees or less;a first bonding medium provided between the first handle substrate andeach of the substrate while maintaining the alignment between referencecrystal orientation and the selected direction of the first handlesubstrate; and a processed region formed overlying each of thesubstrates configured concurrently while being bonded to the firsthandle substrate.
 2. A laser diode device configured from a plurality ofgallium and nitrogen containing semiconductor substrates, each of thegallium and nitrogen containing semiconductor substrates (“substrates”)having a plurality of epitaxially grown layers overlaying a top-side ofeach of the substrates, at least one of the substrates aligned to aspatial region configured in a selected direction of a first handlesubstrate, the first handle substrate having a larger spatial regionthan a sum of a total backside region of plurality of the substrates tobe arranged in a tiled configuration overlying the first handlesubstrate, such that the reference crystal direction for the substrateis parallel to the spatial region in the selected direction within 10degrees or less; a backside region of the substrate, which has beenaligned, mated to a portion of a surface region of the first handlesubstrate; the substrate being bonded to portion of the surface regionof the first handle substrate using a first bonding medium providedbetween the first handle substrate and the substrate while maintainingthe alignment between a reference crystal orientation and the selecteddirection of the first handle substrate, the device comprising a metalcontact and/or a metal bond pad formed to the p-type and/or n-typegallium and nitrogen containing layers.
 3. The device of claim 2 whereinthe reference crystal direction for each of the substrates issubstantially parallel to within 5 degrees or less, parallel to within 3degrees or less, or parallel to within 1 degree or less to the spatialregion configured in the selected direction.
 4. The device of claim 2wherein the reference crystal direction orientation is provided bycleaving the substrate to expose the reference crystal direction, isprovided by X-ray diffraction, or is provided by an orienting flat orotherwise from a determined shape of a portion of the substrate.
 5. Thedevice of claim 2 wherein the first handle substrate is patterned withone or more alignment marks or discontinuous regions of bonding mediaconfigured to align the spatial region to each of the substrates.
 6. Thedevice of claim 2 further comprising, a ridge or some other means ofinducing lateral optical mode confinement to form a laser stripe.
 7. Thedevice of claim 2 further comprising a dielectric passivation layer. 8.The device of claim 2 wherein the gallium and nitrogen containingsubstrate is thinned via lapping or chemical etching.
 9. The device ofclaim 2 further comprising a pair of cleaved region to form facets. 10.The device of claim 2 further comprising a pair of facets, which areopposite of each other, and provided by an etching process selected fromat least one of reactive ion etching (ME), chemical assisted ion beametching (CAIBE), or inductively coupled plasma etching (ICP).
 11. Alaser diode device configured from a gallium and nitrogen containingsemiconductor substrate, the gallium and nitrogen containingsemiconductor substrate (“substrate”) having a plurality of epitaxiallygrown layers overlaying a top-side of the substrate, the substrate beingaligned to a spatial region configured in a selected direction of afirst handle substrate, the substrate being bonded to a portion of thesurface region of the first handle substrate using a first bondingmedium provided between the first handle substrate and the substratewhile maintaining the alignment between a reference crystal orientationand the selected direction of the first handle substrate, the devicecomprising a metal contact and/or a metal bond pad formed to the p-typeand/or n-type gallium and nitrogen containing layers, wherein thereference crystal orientation for the substrate is substantiallyparallel to within 5 degrees or less to the spatial region configured inthe selected direction.
 12. The device of claim 11 wherein the referencecrystal orientation for the substrates is substantially parallel towithin 3 degrees or less, or parallel to within 1 degree or less to thespatial region configured in the selected direction.
 13. The device ofclaim 11 wherein the reference crystal orientation is provided bycleaving the substrate to expose the reference crystal orientation, isprovided by X-ray diffraction, or is provided by an orienting flat orotherwise from a determined shape of a portion of the substrate.
 14. Thedevice of claim 11 wherein the first handle substrate is patterned withone or more alignment marks or discontinuous regions of bonding mediaconfigured to align the spatial region to the substrate.
 15. The deviceof claim 11 further comprising, a ridge or some other means of inducinglateral optical mode confinement to form a laser stripe.
 16. The deviceof claim 11 further comprising a dielectric passivation layer.
 17. Thedevice of claim 11 wherein the gallium and nitrogen containing substrateis thinned via lapping or chemical etching.
 18. The device of claim 11further comprising a pair of cleaved region to form facets.
 19. Thedevice of claim 11 further comprising a pair of facets, which areopposite of each other, and provided by an etching process selected fromat least one of reactive ion etching (RIE), chemical assisted ion beametching (CAIBE), or inductively coupled plasma etching (ICP).